Field of the Invention
This invention relates to a torque transmission apparatus having a vibration damping function.
Description of the Related Art
As a torque converter having a lock-up mechanism, for example, an apparatus having vibration damping function is known, in order to prevent torsional vibration due to engine rotational fluctuation from transmitting directly to a transmission during operation of the lock-up mechanism. Among apparatuses of this type, the apparatus described in Japanese Examined Patent Publication No. 5051447 (JP5051447B) has a first elastic member, a main mass body and a second elastic member serially connected and interposed between a lock-up clutch and turbine runner. In addition, a dynamic damper is formed by connecting an auxiliary mass body to the main mass body through a third elastic member.
Since in an apparatus of this type the lock-up clutch is vibrated at an excitation frequency dependent on engine rotational speed, the excitation frequency is not constant and vibration damping effect should therefore preferably be ensured with respect to a wide range of excitation frequencies. However, since the apparatus described in JP5051447B is structured simply to have the auxiliary mass body connected to the main mass body through the third elastic member, vibration damping effect is exhibited only in the vicinity of excitation frequencies corresponding to the set frequency of the dynamic damper determined by the spring constant of the third elastic member and the inertia of the auxiliary mass body.